Solar Radiation / Light Sensors

Whether you are monitoring solar radiation for agriculture, photovoltaic or energy balance research, you need to select the right sensor for your application.

Light sensors come in a wide range of models and it can be confusing to select the correct one for your application.

  • The most important consideration is what wavelength of light you want to sense. The most commonly used sensor on weather stations is a pyranometer or "total radiation" sensor. These typically measure in the range 400-1100nm which generally relates to visible light. Other sensors measure in the UV, IR (infrared) or other bands.
  • Secondly, you need to know what grade of sensor you require. Pyranometers are graded into three classes according to ISO 9060, and there is a wide range of prices that you will pay depending on the quality. To help decide, you need to think about the how accurate you need the sensor to be for your particular application.
  • Thirdly, you need to think about the environment that you will be using the sensor in. Some sensors are only designed for indoor use (to measure artificial lighting) while others are submersible.
  • Another consideration is what light direction you wish the sensor to respond to. Most sensors are designed to be sensitive to light from a wide angle, but sometimes you may wish to restrict this to incident, or reflected light only. Accessories are also available for specialised studies including fibre optic probes to measure light in very small spaces such as under a plant leaf, or line sensors that average readings from a number of sensors along a single rod for readings under canopy.
  • Finally, you need to consider how you will mount the sensor. Light sensors are designed to be mounted level to ensure the correct response to incoming radiation. They also need to be clear of shading objects.

Global Radiation (Pyranometers)

Measure light in the wavelengths 400-1100nm. The most commonly used light sensor for outdoor studies.
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Direct & Diffuse Radiation

Sensors in this category measure, or calculate incoming short wave radiation, from either direct, or diffuse sources. For direct radiation, a pyrheliometer measures radiation at normal incidence and is mounting on a tracking device which follows the angle of the sun. For diffuse radiation a shade disk or shadow band is used to block out direct radiation.
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Net Radiation (Long & Short Wave)

Measure incoming light in the wavelengths 350-2800nm AND outgoing short wave radiation 4500-100,000nm. Some sensors combine the readings to give one (net) output, while others have multiple outputs to allow maximum analysis.
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Photosynthetically Active Light (PAR)

Quantum Sensors measure radiation in the frequencies used by plants for photosynthesis (400-700nm). Photosynthesis is largely driven by the number of photons between these wavelengths, so this radiation is called the Photosynthetic Photon Flux (PPF) and is measured in µmol m-2 s-1. A quantum is the energy carried by a photon so this is a quantum sensor.
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Light Intensity (Lux)

Typically used for indoor light levels, although some sensors can measure outdoor or underwater levels.
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Ultraviolet (UV)

Measures light in the wavelengths 250-400nm. Some sensors cover the full band while other seperate UVA and UVB.
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Combination & Spectroradiometers


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LI2003S

Solar Sensor Mounts

To make accurate measurements, solar sensors must be mounted where they are not shaded, and either level, or at a specific angle. To achieve this, typically a leveling base and a mounting stand are required.
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